Ultrasonic tools are used in many industries for welding, swaging, and staking, as well as various other activities. In performing these activities it is sometimes necessary to apply a secondary predetermined amount of force to the parts being assembled. Thus, there are occasional non-ultrasonic functions as well as ultrasonic functions to be performed by the same tool. For example, it is often necessary to pre-compress, die cut, perforate, or score a part before, during or after the ultrasonic process.
Conventional nodal mounted ultrasonic welding tools generally utilize a spring-only plunger assembly. The ultrasonic generator sets the horn assembly into resonance along its longitudinal axis, through the introduction of an acoustic converter, in order to transmit mechanical vibrations to the part at a predetermined frequency. The horn assembly typically is a half- or full-wave design for performing ultrasonic operations, and can have a nodal mounted spring actuated plunger mechanism for performing the non-ultrasonic operations. The plunger mechanism is essentially spring biased to stick out of the end of the horn and is typically the first component to contact the part. The horn then continues to move into contact with the part and subsequently welds, stakes, swages (etc.) the part to another part by applying the mechanism vibrations.
There are a number of opportunities for improvement of the above conventional approach. For example, the spring actuated plunger mechanism has a limited range of forces that can be applied to the part. This is a function of the size and tension of the spring. It is therefore desirable to provide an acoustic horn assembly and method that has a wider range of force operation. Another difficulty is associated with the fact that the plunger mechanism is the first component to contact the part and generally cannot be retracted during the welding process. In fact, retraction of the plunger mechanism can only be enabled by retraction of the entire horn assembly. It is commonly known that problems such as part damage and part marking can occur as a result of this phenomenon. It is therefore desirable to provide an acoustic horn assembly having a plunger mechanism that is retractable before, during, or after the ultrasonic welding process.